Gas turbines are known to comprise one or more combustion chambers, wherein a fuel is injected, mixed to an air flow and combusted, to generate high pressure flue gases that are expanded in a turbine.
During operation, pressure oscillations may be generated that could cause mechanical damages to the combustion chamber and limit the operating regime. Nevertheless, frequency of these pressure oscillations may slightly change from gas turbine to gas turbine and, in addition, also for the same gas turbine it may slightly change during gas turbine operation (for example part load, base load, transition etc.).
Mostly gas turbines have to operate in lean mode for compliance to pollution emissions. The burner flame during this mode of operation is extremely sensitive to flow perturbations and can easily couple with dynamics of the combustion chamber to lead to thermo-acoustic instabilities. For this reason, usually combustion chambers are provided with damping devices, such as quarter wave tubes, Helmholtz dampers or acoustic screens, to damp these pressure oscillations.
With reference to FIG. 1, traditional Helmholtz dampers 1 include a damping volume 2 (i.e. a resonator volume) and a neck 3 (an entrance portion) that are connected to a front panel wall 4 (shown by line pattern) of a combustion chamber 5 where a burner 6 is connected. The pressure oscillations generated due to the combustion need to be damped.
The resonance frequency (i.e. the damped frequency) of the Helmholtz damper depends on the geometrical features of the resonator volume 2 and neck 3 and must correspond to the frequency of the pressure oscillations generated in the combustion chamber 5.
Particularly, the volume and neck geometry determine the Eigen frequency of the Helmholtz damper. The maximum damping characteristics of the Helmholtz damper is achieved at the Eigen frequency and it is typically in a very narrow frequency band.
Normally, since the Helmholtz dampers are used to address low frequency range pressure pulsations (50-500 Hz), the volume size of the Helmholtz damper increases. In some cases the volume of Helmholtz damper may even be comparable to burner size. This leaves very little space around the front panel wall 4 for installation of these dampers. Moreover, in order to damp pressure oscillations in a sufficiently large bandwidth, multiple Helmholtz dampers need to be connected to the combustion chamber.
As there is limited space on the front panel wall 4, there are limited options for installation of traditional Helmholtz damper 1. This is shown in FIG. 2, where on front panel wall 4, one burner 6 has to be removed in order to position a Helmholtz damper 1. This eventually is trade off between the number of burners 6 that combustion chamber 5 can accommodate versus the number of traditional Helmholtz damper 1.
Hence, above-mentioned solutions suffer from the space constraint around burner front panel wall for damper installation. Moreover, these solutions do not allow dampers to have a broadband damping frequency in the combustion chamber.